Compositions and Methods for Well Treatment

ABSTRACT

A self-healing cement for use in wells in which carbon dioxide is injected, stored or extracted, comprises a carbonaceous material. In the event of cement-matrix failure, or bonding failure between the cement/casing interface or the cement/borehole-wall interface, the material swells when contacted by carbon dioxide. The swelling seals voids in the cement matrix, or along the bonding interfaces, thereby restoring zonal isolation.

BACKGROUND OF THE INVENTION

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

This disclosure relates to compositions and methods for treatingsubterranean formations, in particular, compositions and methods forcementing and completing wells which penetrate subterranean formations,into which carbon dioxide is injected, stored or extracted.

During the construction of subterranean wells, it is common, during andafter drilling, to place a tubular body in the wellbore. The tubularbody may comprise drillpipe, casing, liner, coiled tubing orcombinations thereof. Usually, a plurality of tubular bodies are placedsequentially and concentrically, with each successive tubular bodyhaving a smaller diameter than the previous tubular body, set atselected depths as drilling progresses. The purpose of the tubular bodyis to support the wellbore and to act as a conduit through whichdesirable fluids from the well may travel and be collected. The tubularbody is normally secured in the well by a cement sheath. The cementsheath provides mechanical support and hydraulic isolation between thezones or layers that the well penetrates. The latter function isimportant because it prevents hydraulic communication between zones thatmay result in contamination. For example, the cement sheath blocksfluids from oil or gas zones from entering the water table and pollutingdrinking water. In addition, to optimize a well's production efficiency,it may be desirable to isolate, for example, a gas-producing zone froman oil-producing zone.

The cement sheath achieves hydraulic isolation because of its lowpermeability. In addition, intimate bonding between the cement sheathand both the tubular body and borehole is necessary to prevent leaks.However, over time the cement sheath can deteriorate and becomepermeable. Alternatively, the bonding between the cement sheath and thetubular body or borehole may become compromised. The principal causes ofdeterioration and debonding include physical stresses associated withtectonic movements, temperature changes and chemical deterioration ofthe cement.

There have been several proposals to deal with the problems ofcement-sheath deterioration. One approach is to design the cement sheathto mechanically survive physical stresses that may be encountered duringits lifetime (U.S. Pat. No. 6,296,057). Another approach is to employadditives that improve the physical properties of the set cement. U.S.Pat. No. 6,458,198 describes the addition amorphous metal fibers toimprove the strength and impact resistance. EP 1129047 and WO 00/37387describe the addition of flexible materials (rubber or polymers) toconfer a degree of flexibility to the cement sheath. WO 01/70646describes cement compositions that are formulated to be less sensitiveto temperature fluctuations during the setting process.

A number of proposals have been made concerning “self-healing” concretesin the construction industry. The concept involves the release ofchemicals inside the set-concrete matrix. The release is triggered bymatrix disruption arising from mechanical or chemical stresses. Thechemicals are designed to restore and maintain the concrete-matrixintegrity. These are described, for example, in U.S. Pat. No. 5,575,841,U.S. Pat. No. 5,660,624, U.S. Pat. No. 6,261,360 and U.S. Pat. No.6,527,849. This concept is also described in the following publication:Dry, CM: “Three designs for the internal release of sealants, adhesivesand waterproofing chemicals into concrete to reduce permeability.”Cement and Concrete Research 30 (2000) 1969-1977. None of these conceptsare immediately applicable to well-cementing operations because of theneed for the cement slurry to be pumpable during placement, and becauseof the temperature and pressure conditions associated with subterraneanwells.

More recently, self-healing cement systems have been developed that aretailored to the mixing, pumping and curing conditions associated withcementing subterranean wells. For example, EP 1623089 describes theaddition of superabsorbent polymers, that may be encapsulated. If thepermeability of the cement matrix rises, or the bonding between thecement sheath and the tubular body or borehole wall is disrupted, thesuperabsorbent polymer becomes exposed to formation fluids. Mostformation fluids contain some water, and the polymer swells upon watercontact. The swelling fills voids in the cement sheath, restoring thelow cement-matrix permeability. Likewise, should the cement/tubular bodyor cement/borehole wall bonds become disrupted, the polymer will swelland restore isolation. WO 2004/101951 describes the addition of rubberparticles that swell when exposed to liquid hydrocarbons. Like thesuperabsorbent polymers, the swelling of the rubber particles restoresand maintains zonal isolation.

Detailed information concerning the performance of self-healing cementsin the oilfield may be found in the following publications: LeRoy-Delage S et al.: “Self-Healing Cement System—A Step Forward inReducing Long-Term Environmental Impact,” paper SPE 128226 (2010);Bouras H et al.: “Responsive Cementing Material Prevents Annular Leaksin Gas Wells,” paper SPE 116757 (2008); Roth J et al.: “InnovativeHydraulic Isolation Material Preserves Well Integrity,” paper SPE 112715(2008); Cavanagh P et al.: “Self-Healing Cement—Novel Technology toAchieve Leak-Free Wells,” paper SPE 105781 (2007).

The aforementioned technologies and publications are mainly concernedwith traditional hydrocarbon producing wells. However, thewell-cementing industry also has to contend with wells into which carbondioxide is injected, in which carbon dioxide is stored or from whichcarbon dioxide is recovered. Carbon dioxide injection is a well-knownenhanced oil recovery (EOR) technique. In addition, there are some oiland gas wells whose reservoirs naturally contain carbon dioxide.

A relatively new category of wells involving carbon dioxide isassociated with carbon-sequestration projects. Carbon sequestration is ageo-engineering technique for the long-term storage of carbon dioxide orother forms of carbon, for various purposes such as the mitigation of“global warming”. Carbon dioxide may be captured as a pure byproduct inprocesses related to petroleum refining or from the flue gases frompower plants that employ fossil fuels. The gas is then usually injectedinto subsurface saline aquifers or depleted oil and gas reservoirs. Oneof the challenges is to trap the carbon dioxide and prevent leakage backto the surface; maintaining a competent and impermeable cement sheath isa critical requirement.

The previously disclosed self-healing cement systems are concerned withtraditional wells and swell when contacted by water and/or hydrocarbons;none of these aims at behavior of the cement sheath when contacted bycarbon dioxide; therefore, despite the valuable contributions of theprior art, there remains a need for a self-healing cement system forwells involving carbon dioxide.

SUMMARY OF THE INVENTION

The present disclosure pertains to improvements by providing cementsystems that are self healing in a carbon-dioxide environment, andmethods by which they may be prepared and applied in subterranean wells.

In an aspect, embodiments relate to the use of a carbonaceous materialin a pumpable cement slurry that ,once pumped downhole, sets to form acement sheath that will self repair when contacted by carbon dioxide.

In a further aspect, embodiments relate to a method for maintainingzonal isolation in a subterranean well into which carbon dioxide isinjected, stored or extracted.

In yet a further aspect, embodiments aim at methods for cementing asubterranean well having a borehole, in which carbon dioxide isinjected, stored or extracted.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any suchactual embodiment, numerous implementation—specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem related and business related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure. In addition, the compositionused/disclosed herein can also comprise some components other than thosecited. In the summary of the invention and this detailed description,each numerical value should be read once as modified by the term “about”(unless already expressly so modified), and then read again as not somodified unless otherwise indicated in context. Also, in the summary ofthe invention and this detailed description, it should be understoodthat a concentration range listed or described as being useful,suitable, or the like, is intended that any and every concentrationwithin the range, including the end points, is to be considered ashaving been stated. For example, “a range of from 1 to 10” is to be readas indicating each and every possible number along the continuum betweenabout 1 and about 10. Thus, even if specific data points within therange, or even no data points within the range, are explicitlyidentified or refer to only a few specific, it is to be understood thatinventors appreciate and understand that any and all data points withinthe range are to be considered to have been specified, and thatinventors possessed knowledge of the entire range and all points withinthe range.

As stated earlier, it would be advantageous to have self-healing cementsystems that operate in an environment containing carbon dioxide. In amanner analogous to the self-healing mechanisms described earlier, suchcement systems would contain materials that swell in the presence ofcarbon dioxide. And, the amount of swelling would have to be sufficientto close voids that may appear in the cement sheath.

In the literature, there are several journal articles concerning theeffects of carbon dioxide on the behavior of coal such as: Busch A etal.: “High-Pressure Sorption of Nitrogen, Carbon Dioxide and theirMixtures on Argonne Premium Coals,” Energy Fuels, 2007, 21 (3)1640-1645; Day S et al.: “Supercritical Gas Sorption on Moist Coals,”International Journal of Coal Geology 74 (2008) 203-214; Day S et al.:Effect of Coal Properties on CO₂ Sorption Capacity Under SupercriticalConditions,” International Journal of Greenhouse Gas Control 2 (2008)342-352; Krooss B M et al.: “High-Pressure Methane and Carbon DioxideAdsorption on Dry and Moisture-Equilibrated Pennsylvanian Coals,”International Journal of Coal Geology, 51 (2002) 69-92; Mazumder, S etal.: “Capillary Pressure and Wettability Behavior of Coal-Water-CarbonDioxide System,” paper SPE 84339 (2003); Ozdemir E et al.: “CO₂Adsorption Capacity of Argonne Premium Coals,” Fuel, 83 (2004)1085-1094; Pan Z et al.: “A Theoretical Model for Gas Adsorption-InducedCoal Swelling,” International Journal of Coal Geology, 69 (2006)243-252; Reucroft P J and Sethuraman A R: “Effect of Pressure on CarbonDioxide Induced Coal Swelling,” Energy Fuels, 1987, 1 (1) 72-75; orSiriwardane H et al.: “Influence of Carbon Dioxide on Coal PermeabilityDetermined by Pressure Transient Methods,” International Journal of CoalGeology, 77 (2009) 109-118.

Most of the references are aimed at studying the feasibility ofsequestering carbon dioxide and other acid gases in coal seams. Thesestudies discuss various advantages and drawbacks of such sequestration;those skilled in the art will appreciate that the chemical environmentassociated with well cementing is far different from that of a coaldeposit. For example, the pH of most hydraulic cements is veryhigh—usually greater than 12. In addition, the formation fluidsencountered downhole are frequently very saline. Salinity and pH areknown to affect the surface behavior of many materials, and the mannerby which the materials interact with external species.

The inventors surprisingly found that certain carbonaceous materials dohave utility in the context of well cementing.

Embodiments relate to methods for maintaining zonal isolation in asubterranean well having a borehole, into which carbon dioxide isinjected, stored or extracted. First, a tubular body is installed insidethe borehole of the well, or inside a previously installed tubular body.Second, a pumpable aqueous cement slurry containing a material thatswells when contacted by carbon dioxide is pumped down the borehole.Then, the slurry is allowed to set and harden. After that, in the eventof cement-matrix failure, or failure of the cement/tubular body orcement/borehole wall bonds, exposing the set cement to wellbore fluidsthat contain carbon dioxide the material will swell and fill voidswithin the cement matrix or at the cement/tubular body orcement/borehole wall interfaces, thereby restoring zonal isolation.

Further embodiments are methods for cementing a subterranean well havinga borehole in which carbon dioxide is injected, stored or extracted.First, a tubular body is installed inside the borehole of the well, orinside a previously installed tubular body. Then, a pumpable aqueouscement slurry containing a material that swells when contacted by carbondioxide is pumped down the borehole. After that, the slurry is allowedto set and harden. Persons skilled in the art will recognize that thisaspect of the invention encompasses both primary and remedial cementingoperations. For primary cementing, the method may be the traditionalprocess of pumping the cement slurry down the casing and up the annulus,or the reverse-cementing process by which the slurry is pumped down theannulus and up the casing. Remedial processes include plug cementing andsqueeze cementing. Plug cementing may be particularly useful when theoperator wishes to safely seal a well containing carbon dioxide. Theremedial processes may be performed in either a cased-hole or open-holeenvironment.

With respect now to further embodiments, methods are disclosed forcementing a subterranean well having a borehole in which carbon dioxideis injected, stored or extracted. First, a tubular body is installedinside the borehole of the well, or inside a previously installedtubular body. Then, a pumpable aqueous cement slurry containing amaterial that swells when contacted by carbon dioxide is pumped down theborehole. After that, the slurry is allowed to set and harden.

For all embodiments, the material may be a carbonaceous material.Preferred materials comprise one or more members of the list comprisingcoal, petroleum coke, graphite and gilsonite. The concentration of thematerial may be between about 5% and 50% by volume of solids in thecement slurry, also known as “by volume of blend (BVOB).” The preferredrange is between about 10% and 40% BVOB. For optimal performance, theparticle-size distribution of the material is preferably such that theminimum d₁₀ is about 100 μm, and the maximum d₉₀ is about 850 μm. Thedefinition of d₁₀ is: the equivalent diameter where 10 wt % of theparticles have a smaller diameter (and hence the remaining 90% iscoarser). The definition of d₉₀ may be derived similarly. Personsskilled in the art will recognize that the present inventive use ofcarbonaceous materials like coal and gilsonite is different and distinctfrom their use as cement extenders (i.e., to reduce the amount of cementor to reduce the cement-slurry density).

In fact, the present disclosure broadly relates to the use of acarbonaceous material in a pumpable cement slurry that once pumpeddownhole sets to form a cement sheath that will self repair whencontacted by carbon dioxide. Preferably the carbonaceous material ispetroleum coke.

For all embodiments the cement may additionally comprise one or moremembers of the list comprising Portland cement, calcium aluminatecement, fly ash, blast furnace slag, lime-silica blends, geopolymers,Sorel cements and chemically bonded phosphate ceramics. The cementslurry may further comprise one or more members of the list comprisingdispersing agents, fluid-loss-control agents, set retarders, setaccelerators and antifoaming agents. Also, the tubular body may compriseone or more members of the list comprising drillpipe, casing, liner andcoiled tubing. In addition the borehole may penetrate at least onefluid-containing reservoir, the reservoir preferably containing fluidwith a carbon dioxide concentration greater than about five moles perliter.

EXAMPLES

The following example are further illustrative:

Example 1

Several particles of petroleum coke were placed inside a pressure cellequipped with a window that allows one to observe the behavior ofmaterials within the cell. The cell supplier is Temco Inc., located inHouston, Tex. USA. The cell temperature is also adjustable. A cameracaptures images from inside the pressure cell, and image-analysissoftware is employed to interpret the behavior of materials inside thecell. After the petroleum coke particles were introduced into the cell,the cell was sealed.

The first test was conducted at 22° C. The particles were allowed toequilibrate at the test temperature for 2 hours. The camera captured animage of the particles. Then, carbon dioxide gas was introduced, and thepressure was gradually increased to 21 MPa. The particles were exposedto the gas for a 2-hour period. The camera captured another image of theparticles inside the cell. The cross-sectional area of the particles wasobserved to increase by 6%.

A second test was conducted at 42° C. The particles were allowed toequilibrate at the test temperature for 2 hours. The camera captured animage of the particles. Then, carbon dioxide gas was introduced, and thepressure was gradually increased to 21 MPa. The particles were exposedto the gas for a 2-hour period. The camera captured another image of theparticles inside the cell. The cross-sectional area of the particles wasobserved to increase by 2.1%.

1. A method comprising: (i) including a carbonaceous material in apumpable cement slurry; (ii) pumping said slurry downhole; (iii)allowing the slurry to set thus forming a cement sheath that will selfrepair when contacted by carbon dioxide.
 2. The method of claim 1,wherein the carbonaceous material is petroleum coke.
 3. A method formaintaining zonal isolation in a subterranean well having a borehole inwhich carbon dioxide is injected, stored or extracted, comprising thefollowing steps: (i) installing a tubular body inside the borehole ofthe well, or inside a previously installed tubular body; (ii) pumpingaqueous cement slurry comprising a material that swells when contactedby carbon dioxide into the borehole; (iii) allowing the cement slurry toset and harden; (iv) in the event of cement-matrix or bonding failure,exposing the set cement to wellbore fluids that contain carbon dioxide;and (v) allowing the material to swell, thereby restoring zonalisolation.
 4. A method for cementing a subterranean well having aborehole in which carbon dioxide is injected, stored or extracted,comprising the following steps: (i) installing a tubular body inside theborehole of the well, or inside a previously installed tubular body;(ii) pumping an aqueous cement slurry comprising a material that swellswhen contacted by carbon dioxide into the borehole; and (iii) allowingthe cement slurry to set and harden inside the annular region.
 5. Themethod of claim 4, wherein the cementing process is primary cementing,and the cement slurry is either pumped down the interior of the tubularbody and up through the annular region, or down the annular region andup the interior of the tubular body.
 6. The method of claim 4, whereinthe cementing process is remedial cementing, performed in either a casedor open hole.
 7. The method of claim 3, wherein the material is acarbonaceous material.
 8. The method of claim 3, wherein the materialcomprises one or more members of the list comprising coal, petroleumcoke, graphite and gilsonite.
 9. The method of claim 3, wherein theconcentration of the material in the cement matrix is between about 5percent and about 50 percent by volume of solid blend (BVOB).
 10. Themethod of claim 3, wherein the concentration of the material in thecement matrix is between about 10 percent and 40 percent by volume ofsolid blend (BVOB).
 11. The method of claim 3, wherein theparticle-size-distribution of the material is such that the minimum d₁₀is about 100 μm, and the maximum d₉₀ is about 850 μm.
 12. The method ofclaim 3, wherein the cement comprises one or more members of the listcomprising Portland cement, calcium aluminate cement, fly ash, blastfurnace slag, lime-silica blends, geopolymers, Sorel cements andchemically bonded phosphate ceramics.
 13. The method of claim 3, whereinthe cement slurry further comprises one or more members of the listcomprising dispersing agents, fluid-loss-control agents, set retarders,set accelerators and antifoaming agents.
 14. The method of claim 3,wherein the tubular body comprises one or more members of the listcomprising drillpipe, casing, liner and coiled tubing.
 15. The method ofclaim 3, wherein the borehole penetrates at least one fluid-containingreservoir, the reservoir containing fluid with a carbon dioxideconcentration greater than about five moles per liter.
 16. The method ofclaim 4, wherein the material comprises one or more members of the listcomprising coal, petroleum coke, graphite and gilsonite.
 17. The methodof claim 4, wherein the concentration of the material in the cementmatrix is between about 5 percent and about 50 percent by volume ofsolid blend (BVOB).
 18. The method of claim 4, wherein theparticle-size-distribution of the material is such that the minimum d₁₀is about 100 μm, and the maximum d₉₀ is about 850 μm.
 19. The method ofclaim 4, wherein the cement comprises one or more members of the listcomprising Portland cement, calcium aluminate cement, fly ash, blastfurnace slag, lime-silica blends, geopolymers, Sorel cements andchemically bonded phosphate ceramics.
 20. The method of claim 4, whereinthe borehole penetrates at least one fluid-containing reservoir, thereservoir containing fluid with a carbon dioxide concentration greaterthan about five moles per liter.